While attending a meeting to get Ritchie into a new school for seventh grade, Christine gets in trouble when she runs into a man who spread some dirty rumors about her when they were in seventh grade themselves.
Christine and Barb give New Christine a bachelorette party in Las Vegas, where New Christine lets all of her previous inhibitions go. Meanwhile, Richard, Matthew, and Richard's brother spend Richard's bachelor party playing laser tag.
Barb and Matthew both move out of Christine's house at the same time, so she tries to prove to everyone that she can make it without them. But was Matthew's decision to move in with his girlfriend a good idea?
There is an outbreak of lice at Richie's school and he is one of the affected ones. Everyone thinks Christine and Richie are "patient zero". Tired of the hassles at that school, Christine looks for another school for Richie.
Christine hooks up with New Christine's dad again before the wedding--and then finds out he's getting married. Also, Matthew finds out his new relationship is temporary, and Barb's new potential beau is forced to arrest her.
Christine considers herself popular by association when Ritchie is asked to a dance by the most popular girl in school, and Matthew and Richard try to evict an elderly woman from the apartment they hope to rent.
Christine only makes things worse when she tries to make amends to a girl she bullied in junior high, while Matthew has a surprise in store for him when he tries to "friend" an ex-girlfriend on Facebook.